1. Field of the Invention
The present invention relates to a method for controlling a molten metal material leaking in an injection apparatus of a metal molding apparatus for a low-melting-point metal material such as magnesium and aluminum.
2. Description of the Prior Art
In an injection apparatus for a low-melting-point metal material, there is provided a slide clearance for an injection plunger between an inner peripheral surface of an injection cylinder and an outer peripheral surface of the injection plunger. Molten metal in a cylinder front portion, which is pressurized by the injection plunger traveling forward during the injection, leaks to this slide clearance. If this leaked material remains at a cylinder rear portion having a temperature lower than that of the cylinder front portion, this leaked material solidifies hard, and constitutes a slide resistance for the injection plunger, thereby adversely influencing the travel of the injection plunger, and a discharge opening for the leaked material is thus provided on the injection cylinder to discharge the leaked material from the slide clearance.
However, there is a low-melting-point metal material such as a magnesium base alloy which ignites if discharged in the atmosphere in a heated state, and there is thus known a molten metal molding apparatus which is provided with a drain storage apparatus with an airtight structure at a discharge opening as means to prevent this, and forms an inert gas atmosphere in the drain storage apparatus to store the metal drain (refer to Japanese Laid-Open Patent Publication No. 2004-291032).
Moreover, there is an injection apparatus which has a circular groove formed at a rear end of an injection cylinder, and solidifies melt, which has flown back in the circular groove, in a somehow soften state by a coolant and a high heat from a heated injection plunger to form a seal member, thereby preventing the backflow (refer to WO2004/018130).
In the process by the drain storage apparatus, a space for the installation is required on the bottom side of the injection cylinder, and since the injection apparatus is usually mounted for forward and backward travel on a machine base, the injection apparatus should be specifically configured so that the drain storage apparatus, which is always connected to an inert gas cylinder, can travel together. Moreover, the leaked material in the slide clearance is directly discharged and recovered, so there is a problem that the material should be measured in consideration of an injection loss by the drain.
Moreover, the molten metal, which has flown back, is solidified in the circular groove in the rear end of the injection cylinder to seal the slide clearance, it is necessary to form a cylinder rear end as a protrusion with a small diameter, to provide the circular groove therein, and to provide a cooling pipe for circulating the coolant in the protrusion with the small diameter, and the structure of the rear end of the injection cylinder thus becomes complicated compared with a conventional injection cylinder. Moreover, since the seal member should be solidified into the somehow soft state by the high heat from both the coolant and the injection plunger, there is also a problem that temperature control relating to the formation of the seal member is difficult.